When an opaque coating such as paint, tile, or terrazzo is applied to a surface, it is usually impossible to determine, by observation of the coating, its thickness. Thickness is important for several reasons. For example, a coating of improper thickness may not perform properly, may not adhere well, or may crack or flake. An excess of organic material represents a definite increase in fire hazard, even when materials of low flammability are used. Aboard ship, an excess of coating material means excess weight, which can be quite significant if deck tile is several layers thick.
Because of the problems of improper thickness, there is a need for a simple, non-destructive means of measuring the thickness of shipboard coatings. The ideal device should be rugged and portable, should be effective whether the coating is over steel or aluminum, and should be useful for typical coatings at typical thicknesses, such as paint (a fraction of a millimeter), tile (a few millimeters), or terrazzo (1 or 2 centimeters). Precision is desirable, but not of great importance, since errors of several percent are not usually very significant.